JP2001125032A - Optical scanning actuator - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an inexpensive optical scanning actuator which is flexible as a whole, by which a large displacement is obtained even when voltage is low and whose optical scanning distance is long. SOLUTION: This optical scanning actuator is constituted of a nearly plate- like actuator equipped with a piezoelectric element 21 obtained by forming a piezoelectric crystal thin film on one side or both sides of a flexible base plate and attaching an electrode to the piezoelectric crystal thin film. One side of the actuator is fixed to support the whole in a cantilever state and the other side is formed as an optical scanning part 31 having an optical scanning means 30 on its surface. The piezoelectric constant of the element 21 is set to 0.1 to 20 pC/N and the flexural rigidity thereof is set to 1.0×10-2 to 1.0×103N.mm.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical scanning actuator which generates a displacement by applying a voltage and thereby performs optical scanning.

[0002]

2. Description of the Related Art In recent years, it has been studied to displace a substance having a relatively small mass or to scan a flow of an electromagnetic wave (especially visible light), a gas, a liquid, or the like by using an actuator which generates a displacement by applying a voltage. , Partially used.

[0003] As the actuator, sintered PZT is used.
Examples include a laminated actuator made of (titanium lead zirconate), a bimorph actuator made of sintered PZT, a monomorph actuator, and an actuator made of an organic film, PVDF (polyvinylidene fluoride).

[0004]

However, the laminated type actuator made of the sintered PZT has a problem that displacement is small. Bimorph-type and monomorph-type actuators made of sintered PZT can increase the displacement as compared with the above-described laminated type, but require a high voltage, and can obtain only a small displacement of about 10 μm at a low voltage of several volts. There is a problem that can not be. The production process of the sintered PZT used for these is complicated, and the number of production days is two.
It takes weeks, so it ’s expensive and uneconomical,
There is also a problem that thinning is difficult. Furthermore, actuators made of PVDF have a problem in that they can be mass-produced and the manufacturing cost is low, but the piezoelectric performance is inferior.

Further, in the case where the above actuator is used as an optical scanning actuator, as shown in FIG. 20, a scanning device having one end of an actuator 100 fixed to a fixed end 101 and a mirror 102 or the like at the other end. Part 10
3 has a problem that the displacement angle of the scanning unit 103 by the actuator cannot be made too large.

The present invention has been made in view of such circumstances, and provides an inexpensive and economical optical scanning actuator capable of obtaining a large displacement even at a low voltage, having a long optical scanning distance. With that purpose.

[0007]

Means for Solving the Problems To achieve the above object,
The optical scanning actuator according to the present invention includes a flexible substrate
A piezoelectric crystal thin film is formed on one or both sides,
Plate shape with a piezoelectric element with electrodes attached to a crystalline thin film
A fixed portion for supporting the entirety of the actuator,
An optical scanning section having optical scanning means on its surface;
The piezoelectric element has a piezoelectric constant of 0.1 to 20 pC / N,
Flexural rigidity 1.0 × 10^-2~ 1.0 × 10 ^ThreeN ・ mm
The configuration is set.

That is, the optical scanning actuator of the present invention uses a piezoelectric element in which a piezoelectric crystal thin film is formed on a flexible substrate, and whose piezoelectric constant and bending rigidity are set within predetermined ranges. , A fixed portion for supporting the entirety and an optical scanning portion having an optical scanning means on its surface are provided in the actuator itself. Therefore, a large displacement can be obtained even at a low voltage, and the optical scanning distance can be increased. And, it can be obtained simply and inexpensively as compared with the conventional structure. Further, since it is thin and substantially plate-shaped as a whole, it can be easily set to an appropriate shape such as an L-shape or a triangular shape, and can have many variations in the optical scanning direction. It has the advantage of being able to.

In the present invention, in particular, when a mass is added to the optical scanning unit, the displacement angle of the optical scanning unit is
It has the advantage that it can be made larger.

In the present invention, in particular, the piezoelectric crystal thin film using a lead-containing composite oxide thin film or the piezoelectric crystal thin film formed by hydrothermal synthesis has particularly excellent performance. ing.

Moreover, among the optical scanning actuators formed by hydrothermal synthesis of the piezoelectric crystal thin film, in particular, the piezoelectric crystal thin film formed by applying a vibration of 3 to 50 Hz in the vertical direction during hydrothermal synthesis. Has very good performance.

[0012]

Next, an embodiment of the present invention will be described.

The optical scanning actuator of the present invention has a structure in which a piezoelectric crystal thin film is formed on one or both surfaces of a flexible substrate, and a piezoelectric element is provided with electrodes attached to the piezoelectric crystal thin film.

The piezoelectric element may be obtained by any method such as a hydrothermal synthesis method, but has a piezoelectric constant of 0.1 to 20 pC / N and a bending rigidity of 1.0 × 10 ^-2. ~
It must be set to 1.0 × 10 ³ N · mm.

The above-mentioned piezoelectric constant is obtained as follows. That is, first, FIGS. 1 (a) and 1 (b)
As shown in FIG. 2 and FIG. 2, the piezoelectric element 21 on which the electrode layer 20 ′ is formed is supported by the fixture 40, and as shown by an arrow in FIG. Apply a load. Then, the displacement of the measurement point Q 1.5 mm inside from the point P is measured by the laser displacement meter, and the output voltage from the piezoelectric crystal thin film on one side is measured by the A / D converter. The measured values (= the ratio of the output voltage peak value to the displacement amount, measured ten times and calculated by the least squares method) obtained in this way, and the structural factors shown in FIGS. And can be calculated by the following equation (1).

[0016]

(Equation 1)

The bending stiffness can be obtained by the following equation (2) using the measured values and the like.

[0018]

(Equation 2)

In order to obtain the piezoelectric element 21 having the above characteristics, it is preferable to form a piezoelectric crystal thin film on the surface of a flexible substrate by a hydrothermal synthesis method.

The flexible substrate has flexibility,
Those that can withstand the heating and pressurizing conditions during hydrothermal synthesis are suitable, and usually, metal thin plates, foils, films and the like are used. Examples of the above metals include metals such as stainless steel, iron, aluminum, titanium, and lead, and alloys containing these metals. However, in order to strongly bond the piezoelectric crystal thin film formed on the flexible substrate to the substrate, it is preferable that the outermost surface of the flexible substrate contains a titanium component. Therefore, it is preferable to use a titanium substrate as the flexible substrate or, if the substrate is not made of titanium, to take measures such as depositing or coating a titanium component on the surface.

The thickness of the flexible substrate is 2 to 20.
It is preferable to set the thickness to 0 μm, especially 5 to 100 μm. That is, when the thickness is less than 2 μm, when obtaining a piezoelectric crystal thin film by hydrothermal synthesis, the flexible substrate may be deformed during hydrothermal synthesis, and when the thickness exceeds 200 μm, the flexibility is poor. This is because it is difficult to obtain a large displacement at a low voltage.

The composition of the piezoelectric crystal thin film may be any composition as long as it has piezoelectric properties, but it is preferable to set the composition to a composition suitable for obtaining by the above-mentioned hydrothermal synthesis. It is. As such a composition,
A composite oxide having a perovskite (ABO ₃ ) structure is exemplified. And, as the above-mentioned site A, usually, Pb, B
a, Ca, Sr, La and Bi at least one element selected from the group consisting of T
i alone or Zr, Zn, Ni, Mg, Co, W, Nb,
A composite of Ti with at least one element selected from Sb, Ta and Fe can be used. Examples of such a composite oxide include Pb (Zr, Ti) O ₃ , PbTi
O ₃ , BaTiO ₃ , SrTiO ₃ , (Pb, La)
(Zr, Ti) O _{3 and the} like, and a piezoelectric crystal thin film containing Pb is particularly preferable.

In the hydrothermal synthesis, usually, an aqueous solution prepared by adjusting an aqueous solution of a metal salt containing a metal element capable of constituting the above composition to alkaline, and a flexible substrate are charged into an autoclave and heated under pressure. It is done by doing. Thereby, a piezoelectric crystal thin film is formed on the front and back surfaces of the flexible substrate (bimorph type). In order to obtain a unimorph type, one side of the flexible substrate is coated with a heat-resistant and alkali-resistant resist material and hydrothermally synthesized, or a piezoelectric crystal thin film formed on the front and back surfaces of the flexible substrate is used. And scrape off one side.

It is preferable that the thickness of the piezoelectric crystal thin film thus obtained is usually set to 0.5 to 100 μm, particularly 1 to 30 μm. That is, the thickness is 0.5μ
m, it is difficult to obtain a sufficient output displacement.
If the thickness exceeds μm, the flexibility of the actuator may be poor even though the flexible substrate is used.

The above-mentioned hydrothermal synthesis is described in Japanese Patent Application Laid-Open No. 4-342.
As disclosed in Japanese Patent Application Laid-Open No. 489/1989, it may be performed in two stages of crystal nucleus generation and crystal growth, or disclosed in JP-A-9-217178 and JP-A-9-27.
As disclosed in Japanese Patent No. 8436, synthesis may be performed in only one step. Further, as disclosed in JP-A-9-278436, the above-mentioned autoclave is
It may be performed while vibrating in the vertical direction. In this case, for example, as shown in FIG. 3, a heating means (not shown)
And heat-resistant container (oil bath or the like) 12 provided with stirring means 11
Inside, the autoclave 10 is vertically movably supported by supporting means 13 and 14, and is 1 Hz or more in the vertical direction, particularly 3 Hz.
It is preferable to perform the hydrothermal synthesis while applying vibration of 50 Hz.

Further, the surface of the flexible substrate-piezoelectric crystal thin film laminate obtained by the above hydrothermal synthesis may be subjected to a sealing treatment (Japanese Patent Application No. 8-277826). The sealing process,
(A) a method of filling a porous portion and a pinhole of a piezoelectric crystal thin film with an insulating material using an insulating material such as a resin or ceramic; and (b) placing the laminate in a high-temperature oxidizing atmosphere and coating with a thin film. A method of forming an insulating oxide film on pinholes that are not covered or have insufficient coating,
Can be performed by any of the methods described above. By this sealing treatment, the performance of the obtained piezoelectric element can be improved.

The insulating material or its precursor used in the above-mentioned sealing treatment may be either organic or inorganic. Examples of the organic material include polyvinyl chloride, polyethylene, polypropylene, polyester, polycarbonate, polyamide, polyimide, epoxy resin, phenol resin, urea resin, acrylic resin, polyacetal, polysulfone, liquid crystal polymer, and PEEK (polyetheretherketone). Is raised. Examples of the inorganic material include a ceramic coating material based on a material such as alumina, zirconia, silica, and titania, and a ceramic precursor such as a metal alkoxide and polysilazane.

After the piezoelectric crystal thin film is formed on both surfaces (or one surface) of the flexible substrate in this way, for example, as shown in FIG. The piezoelectric element 21 can be obtained by forming the electrode layer 20. Reference numeral 15 denotes a flexible substrate.

The electrode layer 20 is formed of Al, Ni, P
This is performed by depositing or coating a conductive material such as t, Au, Ag, or Cu on the surface of the piezoelectric crystal thin film 16. The method is not particularly limited, and for example, application of a conductive paste, electroless plating, sputtering, chemical vapor deposition, or the like can be used. The thickness of the electrode layer 20 is usually preferably set to 1 μm or less, particularly preferably 0.1 μm or less.

As shown in FIG. 5, an optical scanning unit 30 such as a mirror is attached to one end of the surface of the piezoelectric element 21 thus obtained to form an optical scanning unit 31, and the optical scanning unit 30 is attached. As shown in FIG. 6, the opposite end is fixed to the fixed end 32, and the whole is cantilevered, whereby a desired optical scanning actuator can be obtained.

The light scanning means 30 may be any means as long as it reflects light and changes its path. In addition to the mirror, for example, a concave / convex lens or an aluminum vapor-deposited film may be used. it can. As a method of attaching the light scanning means 30, for example, a method of protecting the surface of the piezoelectric element 21 with a protective film or the like, and then attaching the light scanning means 30 thereto via an adhesive is adopted. .

In the optical scanning actuator thus obtained, the piezoelectric element 21 includes the flexible substrate 15, the piezoelectric crystal thin film 16 formed by hydrothermal synthesis, and the electrode layer 20 (see FIG. 4). ), Since its piezoelectric constant and bending stiffness are set within specific ranges, the whole is flexible, large displacement can be obtained even when a low voltage is applied, and the response is fast. Therefore, it can be used for a scanner, a bar code reader, and the like. In particular, a larger displacement can be obtained by using the resonance mode. And it has the advantage that it can be set to a very thin and non-bulky shape, and it is inexpensive and economical due to its simple configuration.

In the above example, the piezoelectric element 21 is constituted by a bimorph type, but is not limited thereto, and may be a unimorph type. In the case of the unimorph type, a metal substrate (such as a titanium substrate) can be used as a back electrode.
It is sufficient to form the electrode layer 20 only on the surface of the substrate.

The method for forming the piezoelectric element 21 is as follows.
Not limited to the hydrothermal synthesis method, any method may be used. However, in order to form a uniform piezoelectric crystal thin film 16 having a thickness of 1 μm or more, as described in Japanese Patent Application Laid-Open No. 9-217178, as described above.
It is most preferable to use a hydrothermal synthesis method as disclosed in JP-A-9-278436 and JP-A-9-278436. In particular, during the hydrothermal synthesis, a vertical vibration to the autoclave 10 is applied within a range of 3 to 50 Hz, and a metal salt (for example, lead nitrate, zirconium oxychloride, titanium tetrachloride) and an alkali (for example, potassium hydroxide) )), The respective concentrations in the mixed aqueous solution can be set as follows, with a piezoelectric constant of 0.1 to 20 pC / N and a bending rigidity of 1.0 ×.
It is particularly suitable for obtaining the piezoelectric element 21 having a characteristic of 10 ^{−2 to} 1.0 × 10 ³ N · mm.

[Preferred Concentrations of Metal Salts and Alkali at the Time of Hydrothermal Synthesis] Lead nitrate 0.1 to 1.0 mol / l Zirconium oxychloride 0.05 to 2.0 mol / l Titanium tetrachloride 0 to 0.5 mol / l Potassium hydroxide 2.5-8.0 mol / L

That is, when lead nitrate falls below the above range,
Since the piezoelectric constant of the piezoelectric element 21 decreases, the output as an optical scanning actuator tends to decrease. Conversely, even if the output exceeds the above range, the piezoelectric constant of the piezoelectric element 21 does not increase. Demerits such as an increase in cost, an increase in by-products, and an increase in the burden on the subsequent washing step tend to increase.

When the zirconium oxychloride falls below the above range, the piezoelectric constant of the piezoelectric element 21 tends to decrease and the output as an optical scanning actuator tends to decrease as in the above case. Beyond
The piezoelectric constant of the piezoelectric element 21 does not increase, and conversely, the disadvantages such as an increase in material cost, an increase in by-products and an increase in the burden on the subsequent cleaning step tend to increase.

Further, when potassium hydroxide is out of the above range, the same tendency as above is observed.

It is not necessary to use titanium tetrachloride when titanium is sufficiently eluted from the flexible substrate 15. However, when titanium is not sufficiently eluted, 0.5 m of titanium tetrachloride is used.
It is preferred that the compounding be performed within a range not exceeding ol / liter. That is, even if titanium tetrachloride is further increased, the piezoelectric constant of the piezoelectric element 21 does not increase, and conversely, the material cost increases, by-products increase, and a burden is imposed on the subsequent cleaning step. This is because there is a tendency for disadvantages to increase.

FIG. 7 shows another example of the present invention. In this optical scanning actuator, an intermediate portion 33 between a portion attached to the fixed end 32 and an optical scanning section 31 to which the optical scanning means 30 is attached is formed with a small width. According to this configuration, when a displacement is applied to the piezoelectric element 21, the optical scanning unit 31 can swing greatly as compared with the configuration in FIG. Can be obtained. As described above, not only making the intermediate portion 33 thinner but also adding a mass to the optical scanning portion 31 such as attaching a weight to the back surface of the optical scanning portion 31 is a point for increasing the displacement.

In FIG. 6 and FIG. 7, one end of the piezoelectric element 21 is attached and fixed to a fixed end 32 made of a separate member. For example, as shown in FIG.
The piezoelectric element 21 can be integrally formed. According to this structure, it is not necessary to attach the piezoelectric element 21 to the fixed end 32 each time. Even when the intermediate portion 33 is formed to have a small width as shown in FIG. Therefore, the manufacturing efficiency is good.

When the fixed end 32 is formed integrally with the piezoelectric element 21 as described above, for example, as shown in FIG.
4 and the optical scanning means 30 such as a mirror
Are attached at predetermined intervals, and the piezoelectric elements 21 indicated by oblique lines
It is preferable that the optical scanning actuator is easily mass-produced by punching in the shape shown in FIG.

Further, the shape of the light scanning unit 31 is not a symmetrical shape but a bulge to one side as shown in FIGS. The scanning unit 31 can be displaced not only in the primary direction but also in the secondary direction (twist direction), so that finer direction control can be performed. In addition, the weight of the light scanning unit 31 can be displaced in the secondary direction in the same manner as described above by attaching a weight to a biased position of the tip of the light scanning unit 31 as it is.

Next, examples will be described together with comparative examples.

[0045]

Examples 1 to 17 Lead nitrate, zirconium oxychloride,
360 ml of a solution of potassium hydroxide and titanium tetrachloride dissolved in water at the ratios shown in Tables 1 to 5 below were placed in a Teflon-lined autoclave container. Also, a titanium foil (titanium substrate) having a predetermined thickness is cut into a predetermined shape,
After washing and drying, it was charged into the above autoclave and sealed. Then, in an oil bath, under pressure, about 150
By performing the hydrothermal synthesis treatment by applying the vibrations shown in Tables 1 to 5 below in the vertical direction at about 48 ° C. for about 48 hours, lead zirconate titanate (PZT) having a predetermined thickness is formed on both sides of the titanium foil.
Was formed. Then, a platinum electrode layer 20 having a thickness of 10 nm was formed on the surface of the PZT layer by an RF sputtering method to obtain a piezoelectric element 21. The shape and dimensions of the piezoelectric element 21 are shown in FIGS.

Then, as shown in FIG. 13, the piezoelectric element 21 is supported by a fixture 50 in a cantilever structure,
The length of the release portion was set to 10 mm. Then, as shown in FIG. 14, an AC power supply frequency characteristic analyzer 52 is connected on the base side of the support portion by using a metal terminal 51 attached to the end of the piezoelectric element 21, and the support portion is connected. The displacement of the edge on the opposite side to the laser displacement meter 5
It was set to be able to measure in 3. The displacement measurement point X is shown in FIG. 15 which is a plan view. The output displacement at the resonance frequency when 1 V was applied and the scanning angle based on the frequency were measured by the AC power supply frequency characteristic analyzer 52.

The scanning angle was measured as follows. That is, first, as shown in FIG.
An aluminum vapor-deposited film 54 for light reflection was attached to the tip of the piezoelectric element
The light is emitted from the light source 55 at an angle of, and the light projection point Y by the reflected light is projected on the screen 56. When the piezoelectric element 21 is displaced, a position Y ′ where the light projection point is at the lowest position (see FIG. 17) and a position Y ″ where the light projection point is at the highest position (see FIG. 18). The angle θ between the two optical paths measured was defined as the “scan angle”. However, for the sake of calculation of the scanning angle, as shown in FIG. 19, an angle θ ′ formed between the optical path in the state where no displacement is given and the optical path at the uppermost position is obtained, and this is doubled to obtain the scanning angle θ. .

The results of these measurements are shown in Tables 1 to 5 below. Further, the voltage required for displacing 100 μm was measured, and those having a required voltage of 10.5 V or less were evaluated as ○ because the characteristics as an optical scanning actuator were excellent. In addition, other criteria (material cost, amount of by-products, etc.) were also judged. Only when both of them were ○, the comprehensive judgment was ○. The results are shown in Tables 1 to 5 below.

[0049]

[Table 1]

[0050]

[Table 2]

[0051]

[Table 3]

[0052]

[Table 4]

[0053]

[Table 5]

[0054]

Comparative Examples 1 to 3 The conditions and the like used for hydrothermal synthesis were changed as shown in Table 6 below to obtain optical scanning actuators as comparative examples. For these, the output displacement was measured in the same manner as described above, and the characteristics and the like as an optical scanning actuator were evaluated. The results are shown in Table 6 below.

[0055]

[Table 6]

[0056]

Comparative Examples 4 and 5 A sintered product (Comparative Example 4) and a PVDF product (Comparative Example 5) having a laminated structure shown in Table 7 below were prepared.
The output displacement was measured in the same manner as above to evaluate the characteristics and the like as the optical scanning actuator. The results are shown in Table 7 below.

[0057]

[Table 7]

[0058]

As described above, in the optical scanning actuator according to the present invention, the piezoelectric element is composed of a flexible substrate and a piezoelectric crystal thin film, and the piezoelectric element has a piezoelectric constant of 0.1 to 20 p.
C / N, flexural rigidity 1.0 × 10 ^{-2 to} 1.0 × 10 ³ N ・
mm, it is flexible as a whole, and generates a large displacement even when a low charge is applied, thereby exhibiting excellent sensitivity and responsiveness. And it has the advantage that it can be set to a very thin and non-bulky shape, and it is inexpensive and economical due to its simple configuration.

[Brief description of the drawings]

FIGS. 1A and 1B are explanatory diagrams of a method for measuring an output voltage of a piezoelectric element.

FIG. 2 is an explanatory diagram of a method for measuring an output voltage of a piezoelectric element.

FIG. 3 is an explanatory diagram of a method for manufacturing a piezoelectric element used in the present invention.

FIG. 4 is an explanatory diagram of a piezoelectric element used in the present invention.

FIG. 5 is an explanatory view showing a state where an optical scanning unit is attached to the piezoelectric element.

FIG. 6 is an explanatory diagram of an optical scanning actuator of the present invention obtained by attaching the piezoelectric element to a fixed end.

FIG. 7 is an explanatory diagram of a modified example of the optical scanning actuator.

FIG. 8 is an explanatory diagram of another modified example of the optical scanning actuator.

FIG. 9 is an explanatory diagram of a manufacturing method of another modified example.

FIGS. 10A and 10B are explanatory diagrams of a modification of the optical scanning unit of the present invention.

FIG. 11 is an explanatory diagram of another modified example of the optical scanning unit of the present invention.

FIG. 12A is a plan view of a piezoelectric element obtained in an example, and FIG. 12B is a front view thereof.

FIG. 13 is an explanatory diagram of a method for measuring output displacement according to the embodiment.

FIG. 14 is an explanatory diagram of a method for measuring an output displacement according to the embodiment.

FIG. 15 is an explanatory diagram of a method of measuring output displacement according to the embodiment.

FIG. 16 is an explanatory diagram of a method of measuring a scanning angle according to the embodiment.

FIG. 17 is an explanatory diagram of a method for measuring a scanning angle according to the embodiment.

FIG. 18 is an explanatory diagram of a method for measuring a scanning angle according to the embodiment.

FIG. 19 is an explanatory diagram of a method for measuring a scanning angle according to the embodiment.

FIG. 20 is an explanatory diagram of a conventional optical scanning actuator.

[Explanation of symbols]

 Reference Signs List 21 piezoelectric element 30 light scanning means 31 light scanning unit

Continuation of the front page (72) Inventor Shingo Hibino 3600, Gezu, Kitai-gaiyama, Komaki-shi, Aichi F-term in Tokai Rubber Industries Co., Ltd. (reference) 2H045 AB81 BA02 BA12 BA18

Claims (5)

[Claims] 1. A substantially plate-shaped actuator having a piezoelectric element in which a piezoelectric crystal thin film is formed on one or both surfaces of a flexible substrate, and an electrode is attached to the piezoelectric crystal thin film. And an optical scanning unit having optical scanning means on the surface, wherein the piezoelectric element has a piezoelectric constant of 0.1 to 20 pC / N and a bending rigidity of 1.0 × 10 ^−2.
An optical scanning actuator, which is set to 1.0 × 10 ³ N · mm. 2. The optical scanning actuator according to claim 1, wherein a mass is added to the optical scanning unit. 3. The optical scanning actuator according to claim 1, wherein the piezoelectric crystal thin film is a composite oxide thin film containing lead. 4. The optical scanning actuator according to claim 1, wherein the piezoelectric crystal thin film is formed by hydrothermal synthesis. 5. The optical scanning actuator according to claim 4, wherein the piezoelectric crystal thin film is formed while applying a vibration of 3 to 50 Hz in a vertical direction during hydrothermal synthesis.